Identification of Toll-like receptor 3 as a potential therapeutic target in clear cell renal cell carcinoma.

PURPOSE Renal cell carcinoma (RCC) is one of the most drug-refractory cancers. The aim of this study is to discover a novel therapeutic target molecule for clear cell RCC (CCRCC), which accounts for the majority of RCC. EXPERIMENTAL DESIGN Gene expression profiles of 27 CCRCCs and 9 normal kidney tissues as well as 15 various adult normal tissues were examined by Affymetrix U133 Plus 2.0 arrays. Among the 34 genes specifically up-regulated in CCRCC, overexpression of Toll-like receptor 3 (TLR3) mRNA and its protein was validated by quantitative reverse transcription-PCR, immunoblot, and immunohistochemistry. The effects of TLR3 signaling on in vitro cell growth were examined. RESULTS TLR3 gene was highly expressed in CCRCC, with only limited expression in a panel of normal tissues. On immunohistochemical analysis using a monoclonal antibody against TLR3, overexpression of TLR3 was observed in 139 of 189 (73.5%) cases of CCRCC as well as in lung metastatic CCRCC (6 of 8), whereas TLR3 expression was entirely absent in chromophobe RCC (0 of 8). Polyinosinic-polycytidilic acid, a TLR3 ligand, exerted a growth-inhibitory effect against RCC cells in a TLR3-dependent manner. Moreover, a combination of polyinosinic-polycytidilic acid and IFNalpha exerted a synergistic growth-inhibitory effect against Caki-1 RCC cells. CONCLUSIONS This is the first report that TLR3 is overexpressed in CCRCC. These observations suggest that TLR3 pathway may represent a novel therapeutic target in CCRCC.